1. Field of the Invention
The present invention relates generally to radio frequency (RF) transceivers.
2. Background Art
Air interface specifications require radio frequency (RF) transmitters to meet a specified error vector magnitude (EVM) performance measured at the antenna of the transmitter. The EVM represents a measure of noise and distortion in a transmitted waveform and is a figure of merit of the transmitter modulation.
Typically, distortion introduced by the power amplifier (PA) of the transmitter is the largest contributor to the EVM measured at the antenna of the transmitter. As such, conventionally, to meet the specified EVM performance, the PA is designed to maintain its output power close to its rated output power over all conditions (i.e., temperature, process, and load impedance variations). This is done by fully characterizing the PA over all conditions (at testing time) and by configuring the PA to operate within a fixed margin from the specified EVM performance so as to accommodate all operating conditions.
While this conventional approach works to maintain EVM compliance by the transmitter, the fixed margin typically increases the power dissipation of the PA beyond what is needed to generate the desired output power under nominal conditions. In addition, the full characterization of the PA at testing time is both costly and time consuming.
The present invention will be described with reference to the accompanying drawings. Generally, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.